The invention relates to self-refrigerating devices employing evaporation/condensation processes. Specifically the invention relates to methods for the preparation of refrigerant materials useful in such devices, and the refrigerant materials resulting from these preparation methods.
Self-refrigerating devices are known in the art. Many products, including liquid products, have more favorable properties when cold than when at ambient temperatures. Thus, cooling of these products to temperatures of between about 0xc2x0 C. and 20xc2x0 C. is desirable. Generally, such cooling is carried out by electrically-powered refrigeration units, or by means of a phase change material such as ice. The use of these units to cool such foods and beverages is not always practical because refrigerators generally require a source of electricity, they are not usually portable, and they do not cool the food or beverage quickly.
An alternate method for providing a cooled material on demand is to use portable insulated containers. However, these containers function merely to maintain the previous temperature of the food or beverage placed inside them, or they require the use of ice cubes to provide the desired cooling effect. When used in conjunction with ice, insulated containers are much more bulky and heavy than the food or beverage. Moreover, in many locations, ice may not be readily available when the cooling action is required.
Ice cubes have also been used independently to cool food or beverages rapidly. However, use of ice independently for cooling is often undesirable because ice may be stored only for limited periods above 0xc2x0 C. Moreover, ice may not be available when the cooling action is desired.
In addition to food and beverage cooling, there are a number of other applications for which a portable cooling device is extremely desirable. These include medical applications, including cooling of tissues or organs; preparation of cold compresses and cryogenic destruction of tissues as part of surgical procedures; industrial applications, including production of cold water or other liquids upon demand; preservation of biological specimens; cooling of protective clothing; and cosmetic applications. A portable cooling apparatus could have widespread utility in all these areas.
Most attempts to build a self-contained miniaturized cooling device have depended on the use of a refrigerant liquid stored at a pressure above atmospheric pressure, so that the refrigerant vapor could be released directly to the atmosphere. Unfortunately, many available refrigerant liquids for such a system are either flammable, toxic, harmful to the environment, or exist in liquid form at such high pressures that they represent an explosion hazard in quantities suitable for the intended purpose. Conversely, other available refrigerant liquids acceptable for discharge into the atmosphere (such as carbon dioxide) have relatively low heat capacities and latent heats of vaporization. As a result, some cooling devices which release carbon dioxide are more bulky than is commercially acceptable for a portable device.
An alternate procedure for providing a cooling effect in a portable device is to absorb or adsorb the refrigerant vapor in a chamber separate from the chamber in which the evaporation takes place. In such a system, the refrigerant liquid boils under reduced pressure in a sealed chamber and absorbs heat from its surroundings. The vapor generated from the boiling liquid is continuously removed from the first chamber and discharged into a second chamber containing a sorbent that absorbs or adsorbs the vapor.
The invention provides methods for the preparation of refrigerant materials used in evaporation/condensation-type self-refrigerating devices, and refrigerant materials which are produced with these methods. The invention is born out of the requirement for high efficiency vaporization of the refrigerant in such devices.
In one aspect, the invention provides a method for preparing an evaporator chamber for use in a portable, single-use, non-releasing evaporation-type refrigerator. The method includes forming a mixture of a volatile non-aqueous solvent (for example, short chain alcohols, including methanol) and a refrigerant dispersant (for example, acrylic-based polymers and copolymers, starch-graft polymers and copolymeric acrylates, including copolymer of acrylamide and an alkali salt of acrylic acid), depositing this mixture (which can be of from about 10 to about 70% by weight of volatile solvent, and from about 30 to about 90% by weight of polymeric material). On the inner surface of an evaporator chamber (in some instances, deposited on substantially the entire inner surface of said evaporator chamber, which, in some circumstances, is covered with a protective lacquer, and which also may be aluminum), over which the refrigerant dispersant is deposited), evaporating the volatile solvent to leave a substantially even coating of refrigerant dispersant on the inner surface of the evaporator chamber, loading the coating of refrigerant dispersant with a refrigerant (for example, water)to produce a substantially even layer of refrigerant intimately associated with the coating of refrigerant dispersant (the layer thickness of refrigerant and dispersant can be up to about 0.03 inches), removing gas from the evaporator chamber by evacuating the evaporator chamber (for example, to a pressure of riot more than about 20 milliTorr), and, sealing the evaporator chamber to prevent re-introduction of gas to the evaporator chamber. The evaporator chamber is also equipped with a means for controlling fluid communication between the interior of the evaporator chamber and an external vessel of lower pressure, for example a sorber chamber separated from the evaporator chamber by a valve and an actuator for preventing fluid communication between the sorber chamber and evaporator chamber until activation of the device. The evaporator chamber is also adapted to provide thermal transfer between its interior and exterior surfaces.
In another aspect, the invention provides a sealed and evacuated evaporator chamber including a gas-tight chamber evacuated to a pressure of not more than about 20 milliTorr, a substantially even layer of refrigerant dispersant coating at least a portion of the inner surface of the gas-tight chamber, a substantially even layer of refrigerant adhered to that layer of refrigerant dispersant; and a means for controlling fluid communication between the interior of the chamber and a lower pressure vessel. The evaporator chamber can be equipped with a means for controlling fluid communication between the interior of the evaporator chamber and an external vessel of lower pressure. The evaporator chamber can be adapted to provide thermal transfer between its interior and exterior surfaces. In another aspect, the invention provides a method of cooling a product with the portable, single-use, non-releasing evaporation-type refrigerator by operating the means for preventing refrigerant vapor flow, thereby permitting this flow. The pressure in the evaporator chamber is reduced subsequent to such operation, causing the refrigerant to vaporize and form a refrigerant vapor, the vapor is collected by the sorbent material in the sorber, and heat is generated in the sorbent. Then, by removing the vapor from the evaporator chamber by collecting the vapor until an equilibrium is reached, where the sorbent is substantially saturated or substantially all the refrigerant has been collected in the sorbent material and containing the heat generated in the sorbent within the sorber by means of the phase change-type heat sink material, the product is cooled.
The invention provides a self-contained and disposable refrigeration device. The device according to the invention does not vent a gas or vapor of any kind. There are no hazardous or toxic materials or components included in the device, and recycling of the materials of the device is facilitated. There are no pressurized gases present in the device and no environmentally objectionable materials such as unstable refrigerants. The device does not explode, even when consumed by fire, and is not flammable.
The methods of refrigerant dispersion provided by the invention are designed to allow for highly efficient and controlled vaporization of refrigerant in portable, single use, non-releasing evaporation-type refrigeration devices. The materials and methods of the present invention allow a substantially even layer of refrigerant to be vaporized from the inner surfaces of evaporator chambers of such refrigeration devices. This substantially even layer of refrigerant is maintained throughout the entire storage life of the refrigeration device despite the influence of gravity and the inevitable jarring that occurs in normal handling of such refrigeration devices.
As used in the specification, a xe2x80x9csubstantially even layerxe2x80x9d refers to layers of refrigerant materials and refrigerant dispersants which are not more than about twice as thick in one location of the surface they cover as in another such location. The refrigerants are to be dispersed on refrigerant dispersants when dispersants are employed, otherwise the refrigerant materials are to be dispersed on the inner surfaces of evaporator chambers, whether the surface is coated or not. The refrigerant dispersants, when employed, are to be dispersed on the inner surfaces of evaporator chambers, whether the surface is coated with any type of protective coating or not. As used in the specification, xe2x80x9cshort chainxe2x80x9d refers to organic molecules containing from one to four carbon atoms. As used in the specification, xe2x80x9ccopolymersxe2x80x9d include both random and block copolymers.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.